1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor including a cylindrical body and a film forming layer formed on an outer surface thereof, having a photosensitive layer. The present invention also relates an image forming apparatus having the electrophotographic photoreceptor.
2. Description of the Related Art
An image forming apparatus such as an electrophotographic copying machine or printer has an electrophotographic photoreceptor and a plurality of processing devices such as a charging device, an exposure device, a development device, a transfer device, a cleaning device and a discharging device, wherein each of them performs a corresponding operation on the electrophotographic photoreceptor and is required for an image formation using the electrophotographic photoreceptor. If an appropriate positional relationship between the processing devices and the electrophotographic photoreceptor is not maintained, it is not difficult to form a required image. Especially, in cases of the charging device and the development device, higher positional accuracies are required in respective distances to the electrophotographic photoreceptor or in respective relative positions thereto along an axial direction of the electrophotographic photoreceptor.
FIGS. 8 and 9 illustrate examples of a conventional method for determining a positional relationship between the electrophotographic photoreceptor and the processing device.
In the example shown in FIG. 8, a processing device 3′ such as a charger or the like is supported by a housing 37′ and, also, a bearing 38′ for rotatably supporting a rotation axis 28′ of an electrophotographic photoreceptor 2′ is provided at both end portions of the housing 37′. The processing device 3′ is provided with rollers 39′ that can rotate while being in contact with an outer surface of the electrophotographic photoreceptor 2′. Further, in the example shown in FIG. 8, an appropriate distance between the electrophotographic photoreceptor 2′ and the processing device 3′ can be maintained during the rotation of the electrophotographic photoreceptor 2′ due to the presence of rollers 39′ that can rotate while being in contact with the outer surface of the electrophotographic photoreceptor 2′.
Meanwhile, in the example shown in FIG. 9, an electrophotographic photoreceptor 2″ has both end portions of tapered shapes in which respective diameters increase gradually toward the end portions, and butting rollers 59″ of a processing device (development device) 5″ are made to rotate while being in contact with tapered portions 29″ (see, e.g., Japanese Patent Laid-open Application No. H10-63142). Moreover, in the example shown in FIG. 9, the diameters of the tapered portions 29″ increase gradually toward the end portions, so that the butting rollers 59″ can be prevented from being misaligned with respect to the axial direction of the electrophotographic photoreceptor 2″. As a result, it is possible to maintain an appropriate distance between the electrophotographic photoreceptor 2″ and the processing device (development device) 5″ and further to avoid the misalignment in its position along the axial direction.
However, in the example shown in FIG. 8, the processing device 3′, e.g., a charger or the like, and the electrophotographic photoreceptor 2′ (rotation axis 28′) need to be positioned and supported with respect to the housing 37′; the rollers 39′ of the processing device 3′ need to be positioned and supported with respect to the processing device 3′; and the housing 37′ itself needs to be positioned and supported. As a consequence, it is not easy to maintain an appropriate positional relationship between the electrophotographic photoreceptor 2′ and the processing device 3′. Besides, in order to improve the positional accuracy, the cost required for the positioning increases. If the housing 37′ is used for the positioning, a space for the housing 37′ is required, which scales up the apparatus.
Meanwhile, in the example shown in FIG. 9, the butting rollers 59″ of the processing device (development device) 5″ are made to rotate while being in contact with the tapered portions of the electrophotographic photoreceptor 2″, so that the positional accuracy can be improved with a simple structure and at a low cost. On the other hand, impurities such as abrasive particles and the like can be produced from the electrophotographic photoreceptor 2″ or the butting rollers 59″ due to friction, contact rotation or the like between the tapered portions 29″ of the electrophotographic photoreceptor 2″ and the butting rollers 59″. In that case, since the tapered portions 29″ are formed so that the diameters decrease gradually toward a central portion (latent image forming region) of the electrophotographic photoreceptor 2′, the impurities such as abrasive particles and the like can easily be dispersed to be left in the latent image forming region. When the impurities are dispersed to be left in the latent image forming region, they are adhered to the latent image forming region, thereby deteriorating quality of the image.